As a gasket used as a sealing means at a connecting portion or the like of a case, there is a known gasket integrally including a pair of seal beads positioned at both axial ends of a gasket body and oriented to an inner peripheral side in directions axially opposing to each other (Patent Document 1).
The inventor of the present application proposes a structure illustrated in FIG. 5 as the gasket integrally including such a pair of seal beads.
This gasket 100 has a structure in which a gasket body 102 formed of a rubber-like elastic material (rubber material or synthetic resin material having rubber-like elasticity) is integrally molded with a metallic reinforcement ring 101. The gasket body 102 is integrally molded with a pair of seal beads 102a, 102b positioned at both axial ends thereof and oriented to an inner peripheral side in directions axially opposing to each other. The seal beads 102a, 102b are formed so as to have almost same shape and substantially same rigidity.
The gasket 100 is disposed inside a setting groove 201 formed at an opening edge portion of one member 200 constituting a sealing target space S. Further, clearance δ between the members 200 and 300 is sealed when the gasket 100 is axially compressed between an end surface 201a of the setting groove 201 and an end surface 300a of the other member 300.
Here, while the gasket 100 is set, the axial compression force applied to the gasket 100 acts as force F that causes the seal beads 102a, 102b of the gasket 100 to fall toward the inner peripheral side. On the other hand, fluid pressure P inside the sealing target space S acts as force that causes the seal beads 102a, 102b to closely contact the end surfaces 300a and 201a when inner peripheral surfaces of the seal beads 102a, 102b receive the fluid pressure P. By this, the gasket 100 exerts a self-sealing function by the seal beads 102a, 102b, and seals the clearance δ between the members 200 and 300.
However, in the case where the fluid pressure P inside the sealing target space S is high, the gasket 100 sometimes makes movement as illustrated in FIG. 6 in which its setting position inside the setting groove 201 is axially displaced to one of the seal beads (seal bead 102a in FIG. 6) having lower rigidity because of a slight rigidity difference between the two seal beads 102a, 102b. In this case, the seal bead having reduced interference (seal bead 102b in FIG. 6) is largely deformed toward an outer peripheral side by the fluid pressure P in a manner protruding toward the clearance δ, and fluids inside the sealing target space S may leak out as indicated by a dotted arrow.
Further, when the fluid pressure is repeatedly turned on and off, the seal beads 102a, 102b may be abraded as a result of a fact that the gasket 100 repeats axial displacement to one side and recovery movement to an original position with a large stroke inside the setting groove 201.
On the other hand, there is another gasket disclosed in Patent Document 2 in which a gasket body is integrally molded with a reinforcement ring and a pair of lip portions positioned at both axial ends is formed to have different thicknesses respectively.
This gasket is disposed such that the reinforcement ring is eccentrically located on one axial end side, and an inserting direction of the gasket into a setting groove is specified such that the reinforcement ring is disposed at a position to block a clearance between mating members. Further, the thickness of one of the lip portions disposed on the reinforcement ring side is formed thinner than the thickness of the other lip portion, thereby more largely deforming the thinner lip portion disposed on the reinforcement ring side when the gasket is axially compressed inside the setting groove. By this, the gasket is axially positioned such that the reinforcement ring constantly blocks the clearance, and protrusion of the lip portion toward the clearance can be surely prevented by the reinforcement ring.